This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A173459 #13 Feb 24 2021 02:48:19 %S A173459 2,3,1,7,9,1,7,9,3,21,27,1,7,9,3,21,27,3,21,27,9,63,81,1,7,9,3,21,27, %T A173459 3,21,27,9,63,81,3,21,27,9,63,81,9,63,81,27,189,243,1,7,9,3,21,27,3, %U A173459 21,27,9,63,81,3,21,27,9,63,81,9,63,81,27,189,243,3 %N A173459 a(n) = A173457(n+1)/4. %H A173459 David Applegate, Omar E. Pol and N. J. A. Sloane, <a href="/A000695/a000695_1.pdf">The Toothpick Sequence and Other Sequences from Cellular Automata</a>, Congressus Numerantium, Vol. 206 (2010), 157-191. [There is a typo in Theorem 6: (13) should read u(n) = 4.3^(wt(n-1)-1) for n >= 2.] %H A173459 N. J. A. Sloane, <a href="/wiki/Catalog_of_Toothpick_and_CA_Sequences_in_OEIS">Catalog of Toothpick and Cellular Automata Sequences in the OEIS</a> %e A173459 From Omar E. Pol, Apr 22 2013 (Start): %e A173459 When written as an irregular triangle begins: %e A173459 2,3; %e A173459 1,7,9; %e A173459 1,7,9,3,21,27; %e A173459 1,7,9,3,21,27,3,21,27,9,63,81; %e A173459 1,7,9,3,21,27,3,21,27,9,63,81,3,21,27,9,63,81,9,63,81,27,189,243; %e A173459 1,7,9,3,21,27,3,21,27,9,63,81,3,21,27,9,63,81,9,63,81,27,189,243,3,... %e A173459 (End) %Y A173459 Cf. A173456, A173457, A173458, A173463. %K A173459 nonn,tabf %O A173459 1,1 %A A173459 _Omar E. Pol_, Feb 18 2010 %E A173459 a(13)-a(72) from _Lars Blomberg_, Apr 22 2013